A known constant velocity joint comprises an outer part formed centered on an axis with three radially inwardly open and axially extending channels each having a pair of angularly confronting and axially extending inner running surfaces or tracks that are each concave toward the other inner running surface of the respective pair, an inner part formed centered on a respective axis with three radially outwardly projecting trunnions each engaged in a respective one of the channels and defining respective radially extending trunnion axes, and respective annular rollers rotatable on the trunnions about the respective trunnion axes and having outer running surfaces riding on the inner running surfaces of the respective channels and each radially outwardly convex relative to the respective trunnion axis. On rotation of the joint with the inner and outer members relatively angled, the rollers move along the tracks with a superimposed pivotal moment which gives rise to track friction. The track friction essentially consists of two components, the track friction force due to the linear movement of the rollers and the frictional movement of the bore friction due to the pivotal movement.
The combined frictional forces of all three rollers result in a periodic axial force of third order. If the joint is used in, for example, the drive train of a vehicle, undesired vibrations or shocks are caused by the periodic axial forces, which are also called shaking forces. The axial force of the bore friction acts in opposite direction to the shaking forces, such that if the bore friction is increased the resultant shaking forces are reduced.
For optimizing travel smoothness, easy movement of a joint is, in some circumstances, at least as important as reducing the shaking forces. The easier the movement of the joint, the better the insulation of the vibrations emanating from, for example, the vehicle engine. Even when there is no transmission of torque through the joint, the easy movability of the joint with the vehicle stationary is important, as the joint provides a measure of insulation of the shaking caused by the running engine.
In German patent document 2,157,372 there is disclosed a joint in which each roller consists of two halves urged apart radially of the Joint and against the track flanks by means of a spring. In the case of higher levels of torque, the roller halves are rigidly interconnected, in which case line contact with a short interruption is present.
German patent document 2,234,236 discloses a similar joint construction in which two-point contact at higher torque values occurs as a result of modification of at least one outline of the contact surfaces. In a further construction, a longitudinal groove is provided in the roller track. This serves to prevent excessive pressure on the inward acute-angled edges of the roller halves and to ensure free pivotal mobility of the roller.
The division of each roller into two relatively rotatable halves can lead to appreciable reduction in bore friction and thereby to an increase in the shaking forces or at least to an unstable behavior thereof. The pivotal movement of the roller is translated not into an opposite sliding on the track flanks, but into a relative rotation of the roller halves in the manner of a slipping clutch so that only slight bore friction is produced. The force component urging the roller halves together is appreciably less than the normal transmission force between the roller halves and the track flanks. Moreover, the lever arm, which comes into effect on the relative rotation of the roller halves, of this slipping-clutch system is smaller than that of the track flanks, and an undesired build-up of heat also results from relative rotation of the two halves.
The division of the roller, which is the source of inaccuracies and additional costs, is thus disadvantageous in these forms of construction. In addition, with respect to the condition in which no or only low torque is transmitted through the joint, the four-point contact between each roller and its track results in undesired stiff movement of the joint.
The conformity of the point contact, which occurs at higher torque values in the joint according to the above-mentioned German patent document 2,234,236, is decisively lower by comparison with the conformity of a line contact. Surface pressure is thereby significantly higher and wear and service life appreciably worse. The formation of a separating lubricant film is reduced, the values of the track friction increased and the easy movability of the joint is diminished.